Ignition circuits



J. W. MOTTO, JR.. ETAL IGNITION CIRCUITS Filed July 23, 1964 '0 TO SPARK DISTRIBUTING WITNESSES Ill INVENTORS John W. Movto,Jr. and

Warren C. Fry

United States Patent 3,308,800 IGNITION CIRCUITS John W. Motto, Jr., Greensburg, and Warren C. Fry,

Connellsville, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed July 23, 1964, Ser. No. 384,656 6 Claims. (Cl. 123148) The present invention relates to ignition circuits, and more particularly to ignition circuits utilizing semiconductor switching devices.

By far the most commonly used ignition system in au tomobiles of today is the mechanical breaker-type. The mechanical breaker ignition system introduces several limitations in the functioning of an internal combustion engine. Among these limitations the most severe ones are: low life expectancy of the mechanical breaker points; lost spark energy due to poor switching of breaker points during start-up and as the points degradate; and attenuation of spark voltage at high engine speeds. The probable life expectancy of presently used mechanical breaker points is typically 10,000 miles. This limited life expectancy is principally due to the mechanical switching operation and the arching produced between the ignition points. Ignition points as commonly used in automobile engines operate at approximately 300 to 400 volts and carry currents of the order of 3 to 6 amperes. At such voltages and currents the points are quickly degraded by the severity of arcing produced. Furthermore, with even a partial degradation of the ignition points, for example after 5000 miles of usage, a substantial impairment in the efficiency of operation of the engine will result. The reason for this is that spark energy is lost by poor switching of the breaker points after the points have been somewhat degraded. This degradation also results in lack of uniformity in spark output. This problem is especially severe during the cranking or start-up of the engine with the breaker points being switched at relatively low speeds and a large amount of spark energy being required to start the engine.

Modern automobile engines require higher engine speeds as dictated by increased efficiency and horsepower requirements of the engines. At higher r.p.m.s severe requirements are placed on the ignition system to supply a large enough spark voltage within a limited time. In the usual case, a set of ignition points are open for onehalf of the cycle, while energy is being supplied to the ignition coil; and the ignition points are closed for the second half of the cycle, while the spark energy is being supplied to the distributor circut. Thus, as engine speed increases, there is less time for energy to be supplied to the ignition coil and, therefore, less energy to be dissipated in the distributor and spark plug arrangement. It can, therefore, readily be seen that as the speed of the engine increases, the quality and magnitude of the spark voltage will decrease and detract from the efficiency of operation in that it will be more diificult to adequately fire the spark plugs with only the limited amount of spark voltage applied thereto.

These disadvantages and limitations of mechanical breaker point ignitionsystems may be overcome through the use of ignition circuits using a semiconductor device, termed herein as a gate controlled switch (GCS). The gate controlled switch, or as it is sometimes called a semiconductor thyratrou or a semiconductor switch having a gate turn-off characteristic, is a four layer, three terminal, solid state switching device having characteristics similar to those of the conventional silicon controlled rectifier (SCR). The GCS possesses the desirable characteristics of the SCR such as: high blocking voltages, high surge ratings and pulse turn-on, but, moreover, the GCS has a unique ability of being turned off by the application of a negative pulse voltage to its gate electrode, without the necessity of reducing the anode cathode current to below the hold value. This unusual gate turn-off characteristic provides very desirable results when utilized in ignition circuits as will be fully discussed herein.

It is, therefore, an object of the present invention to provide a new and improved ignition circuit utilizing a gate controlled switch.

It is a further object of the present invention to provide a new and improved ignition circuit utilizing gate cciafntrolled switches which may rapidly be turned on and o It is a further object of the present invention to provide a new and improved ignition circuit utilizing a gate controlled switch which provides long lifetime for breaker points, low loss in spark energy and small attenuation of spark voltage at high engine speeds.

The above-cited objects are accomplished in an ignition circuit wherein, a gate controlled switch is rendered non-conductive by the closing of a set of ignition points and the discharge of energy storage devices operative with the gate controlled switch. By the breaking of the circuit including the gate controlled switch a voltage is induced in an ignition coil to be transferred as a spark output voltage. The energy storage devices are recharged when the ignition points are reopened.

These and other objects and advantages of the present invention will become more apparent when considered in view of the following specification and drawings, in which:

FIGURE 1 is a schematic diagram of one embodiment of the ignition circuit of the present invention; and

FIG. 2 is a schematic diagram of another embodiment of the ignition circuit of the present invention.

Referring to FIG. 1, it is assumed initially that an olfrun switch S0 is in its closed run position and a set of ignition points Si are in their open position. The set of ignition points Si are shown schematically and may, for example, be the common mechanical breaker-type which open and close in timed sequence in response to the rotation of the cam shaft of an internal combustion engine. With the switches So and Si in the state shown, a gate controlled switch G will be in its conductive, turned-on state. The gate controlled switch G includes an anode electrode a, a cathode electrode k, and a gate electrode g. The cathode electrode k of the gate controlled switch G is grounded. The anode electrode a is connected to an ignition transformer IT through a primary winding or coil W1 thereof. The other end of the primary winding W1 is connected through a current limiting resistor R1 to one end of the off-run switch S0. The other end of the switch S0 is connected to the positive electrode of a battery E. The negative electrode of the battery E is grounded. The battery E may, for example, be a twelve volt multicell type commonly used in automobiles. Thus, upon closing the off-run switch S0 electrical energy is supplied into the ignition circuit from the battery E.

To render the gate controlled switch G conductive, a positive voltage is applied to the gate electrode g. This is done by charging a capacitor C1 connected to the gate electrode g to the polarity as shown in FIG. 1. A charging circuit including a series combination of an inductor coil L1 and a diode D1 is connected through the off-run switch S0 to the positive end of the battery E. The diode D1 has its cathode electrode connected to the positively charged side of the capacitor C1. Thus, once the capacitor C1 is charged the diode D1 will maintain this charge. The capacitor C1 is charged to the polarity as shown. Also connected to the positively charged end of the capacitor C1 is a discharge resistor R2, which has its other end connected to one side of the set of ignition points Si. The other side of the set of ignition points Si is grounded. Connected between the anode electrode a of the gate controlled switch G and the ungrounded end of the set of ignition points Si is a capacitor C2. The capacitor C2 aids in the turning off of the gate controlled switch G by shunting the current away from the anode electrode a so as to reduce the anode-cathode current of the gate controlled switch G.

Upon closing the set of ignition points Si, the capacitor C1 will discharge through the resistor R2 and the ignition switch Si to ground. This will withdraw current from the gate circuit of the gate controlled switch G and, therefore, turn 01f the-gate controlled switch G. Also the capacitor C2 will discharge through the set of ignition points Si to ground. The elfect of the discharge of the capacitor C2 will be to lower the anode-cathode current of the gate controlled switch G by shunting current from the anode electrode a of the gate controlled switch and, therefore, aid in the turning off of the gate controlled switch. The use of the capacitor C2 may be necessary under adverse operating conditions when an extremely large current is being drawn by the gate controlled switch G. Therefore, by the combined discharge of the capacitor C1, drawing current from the gate electrode g, and the discharge of the capacitor C2, drawing current from the anode electrode a, the gate controlled switch G will rapidly turn oil even under the most adverse conditions. The gate controlled switch has a typical turn-oh time of the order of 3 microseconds, which is extremely fast compared to mechanical switching operations.

The sudden breaking of the anode-cathode circuit of the gate controlled switch G will cause a high voltage to be induced in the primary coil W1 of the ignition transformer IT in order to counteract the rapid change of current in this circuit. The transformer IT may, for example, be a step-up ignition transformer commonly used in automobile ignition circuits. A high output spark voltage will be induced in a secondary ignition winding or coil W2 of the transformer IT. One end of the secondary coil W2 is connected to the bottom end of the primary ignition coil W1, with an output terminal To being connected to the other end of the coil W2 to supply an output spark volt age, for example, to a spark distribution circuit, not shown. The high output voltage from the secondary ignition W2 is ultimately supplied to spark plugs of an internal combustion engine to fire the respective spark plugs in timed sequence.

When the'set of ignition points Si are reopened, a voltage is induced in the inductor coil L1 due to the sudden change of current in the charging circuit.. The capacitor C1 is recharged by the voltage induced in the inductor L1 to the polarity as shown to render the controlled switch G conductive by the application of a positive pulse to the gate electrode g. V The capacitor C2 is also charged at this time to the polarity as shown to be ready to aid in the turning off of the gate controlled switch G when the set of ignition points are again closed.

The circuit components are so selected that the capacitor C1 will charge to a voltage of approximately 30 volts and the capacitor C2 to a somewhat lower voltage. Approximately one ampere will pass through the switch Si through the combined discharge of the capacitor C1, through the resistor R2, and the capacitor C2. Comparing these values to the three to six amperes at 300 to 400 volts usually applied to mechanical ignition points, it can readily be seen that the present system will have a substantially longer lifetime. It has been shown by tests that circuits of the type presently disclosed have a lifetime of approximately five times that of the ordinary breaker ignition point system.

It should also be noted that improved life ignition points will be obtained because of the substantially similar turnoff and turn-on characteristic of the gate controlled switch G for each of the cycle-s. Thus, the ignition points will open and close under substantially similar conditions which will tend to limit any wide variation in arcing conditions and, therefore, attenuate degradation of the points even after substantial usage.

FIG. 2 shows an ignition circuit providing improved performance at high engine r.p.m.s. The circuit of FIG. 2 has a similar arrangement as that of FIG. 1 except that a resistor R3 is connected between the gate electrode g of the gate controlled amplifier G across the primary winding W1 of the ignition transformer IT. Thus, a positive bias potential is continuously provided to the gate electrode g from the battery E through the resistors R1 and R3. This biasing potential isselected to provide sufiicient potential to maintain the gate controlled switch G in its conductive state. Thus, in the absence of a negative pulse being provided to the gate electrode g by the discharge of the capacitor C1, the gate controlled switch G will always be in its conductive state independent of the position of the set of ignition points Si whether open or closed.

In the typical ignition system the ratio of on time (the time during which a spark output voltage is provided by the system) to off time (the time when energy is being stored in the system) is approximately one. It has been found that 200 microseconds is a suflicient period to supply adequately the spark output voltage from the secondary ignition coil. Even at 5000 rpm. in an eightcylinder engine, the time between sparks is approximately 3 milliseconds. The time constant (L/R) of a typical primary ignition coil is approximately 2 milliseconds. It can thus be seen under the assumed conditions that the primary ignition coil will not be carrying full current at the end of a half cycle of 1.5 milliseconds during which a conductive path is provided therethrough. 'When the circuit including the ignition coil is opened, since the primary ignition coil will not be carrying full current because of its time constant, a smaller output spark voltage Will be supplied from the secondary ignition coil than would be supplied at lower engine speeds. Therefore, this results in an attenuation of the output pulse and poor operation of the engine at high speeds.

In the circuit of FIG. 2, this problem is averted by maintaining the gate controlled switch G conductive during all of the switching cycle except for the period while the capacitor C1 discharges through the resistor R2. The discharge time of the capacitor C1 may be selected to be the time required to generate a sufficient output spark voltage from the secondary ignition coil W2, that is, ap= proximately 200 microseconds in the. present example. Thus, during the remainder of the period, that is, 3 milli= seconds minus 200 microsecondsiat 5000 rpm. for an eight cylinder engine), the gate controlled switch '6 will be conductive to permit the primary winding W1 to build up current all during this time period. With a typical time constant (L/R) of 2 milliseconds for a standard ignition coil, it can be seen that the current in the primary ignition winding W1 will have reached substantially its steady state value before the gate controlled switch is turned off. In other words, when capacitor C1 is again discharged to apply a negative pulse to the gate electrode G, the primary coil W1 will be carrying a relatively high current; Thus, a high output voltage will be generated at the output winding W2 to supply a high magnitude spark output voltage to the respective spark plugs even at high engine speeds. The sequence of operation of the circuit of FIG. 2 is thus: with ignition switch Si open and the capacitors C1 and C2 charged as shown, the gate controlled switch G will be in its conductive state with current flowing through the primary ignition coil W1. When the switch Si is closed, the capacitors C1 and-C2 will discharge, through the switch Si to render the gate controlled switch non-conductive in the same manner as explained with reference to FIG. 1. The time constant. of the discharge circuit, including the capacitor C1 and the resistor R2, is so selected that the spark output voltage. taken from the output winding W2 will have substantially.-

terminated before the negative pulse from the capacitor C1 is taken away from the gate electrode g. This time as discussed above is approximately 200 microseconds. After the negative pulse from the capacitor C1 is removed by the substantially complete discharge of the capacitor C1 through the resistor R2 to ground, the gate controlled switch G is turned on again by a positive potential being applied to the gate electrode g through the biasing resistor R3. Current may then build up again through the primary ignition coil W1, a conductive path being provided through the anode-cathode circuit of the gate controlled switch G to ground. It should be noted at this time the ignition points are still in their closed position. The ignition points Si will not open until the half cycle has been completed. All during this time, however, current is building up in the primary winding W1. At the end of the half cycle, the ignition points Si will open which will induce a voltage in the conductor coil L1 which, in turn, will charge the capacitors C1 and C2 to the polarities as shown on the drawing. The capacitors C1 and C2 are now recharged to be in a state so that the capacitor C1 can apply a negative pulse to the gate electrode g upon the closing of the set of ignition points Si. At the end of the second half cycle, the firing cycle is repeated by closing of the set of ignition points Si. The capacitor C1 then discharges through the resistor R2 to ground applying a negative pulse to the gate electrode g which overcomes the positive potential applied thereto through the resistor R3. The gate controlled switch G is thus turned off by this negative pulse with the turning oil? also being aided by the discharge of the capacitor C2 drawing current from the anode electrode to ground.

By the above-described sequence of operation, it can readily be seen that better high speed operation of an internal combustion engine will result since the gate controlled switch G is in its conductive state during all but approximately 200 microseconds of a cycle, which may be of the order of 3 milliseconds for an eight-cylinder engine at 5000 rpm. Because of this substantially longer conductive period, the primary ignition coil will have time to build up current to a substantially larger value. Thus, a larger amount of energy will be permitted to be transferred to the secondary winding W2 as an output spark voltage in that the amount of energy capable of being stored in the primary coil is dependent upon the square of the current passing therethrough. The circuit of FIG. 2 also, of course, provides the attendant advantages as discussed in relationship to FIG. 1.

Although the present invention has been described with a certain degree of particularity, it should be understood that the present disclosure has been made only by way of example and that numerous changes in the details of circuitry and the combination arrangement of parts and elements may be resorted to without departing from the scope and spirit of the present invention.

We claim is our invention:

1. An ignition circuit comprising, a gate control switch including a plurality of electrodes, an ignition transformer including a primary winding operatively connected in sereis with said gate controlled switch and a secondary output Winding, a first capacitive device operatively connected to one electrode of said gate controlled switch, a second capacitive device operatively connected to another electrode of said gate controlled switch, a charging circuit operatively connected to said first and second capacitive devices to charge said first and second capacitive devices, a set of ignition points operatively connected to said first and second capacitive devices, upon closing said set of ignition points said first and second capacitive devices discharging therethrough to render said gate controlled switch non-conductive, with a voltage being induced in said primary winding of said ignition transformer by the gate controlled switch being rendered non-conductive, an output spark voltage being provided in said secondary out- 6 put winding in response to the induced voltage in said pri-' mary winding, upon opening said set of ignition points a voltage being induced in said charging circuit to recharge said first and second capacitive devices.

2. An ignition circuit operative with a source of direct current comprising a gate controlled switch including an anode-cathode circuit and a gate circuit, an ignition transformer including a primary winding operatively connected in said anode-cathode circuit and a secondary winding, a first capacitive device operatively connected in the gate circuit, a second capacitive device operatively connected in the anode-cathode circuit, a charging circuit operatively connected to said first and second capacitive devices to charge said first and second capacitors, switching means operatively connected to said first and second capacitive devices, upon closing said switching means said first and second capacitive devices discharging therethrough to render said gate controlled switch non-conductive, a voltage being induced in said primary winding of said ignition transformer by the gate controlled switch being rendered non-conductive, an output spark voltage being provided in said secondary output winding in response to the induced voltage in said primary winding, upon opening said switching means a voltage being induced in said charging circuit to recharge said first and second capacitive devices to render said gate controlled switch conductive.

3. An ignition circuit operative with a source of direct current comprising a gate controlled switch including anodes, cathode and gate electrodes, said cathode electrode operatively connected to a reference potential, an ignition transformerincluding a primary winding operatively connected in series to said anode electrode and a secondary output winding, a first capacitive device operatively connected to the gate electrode of said gate controlled switch, a second capacitive device operatively connected to the anode electrode of said gate controlled switch, a charging circuit including an inductive device operatively connected to said first and second capacitive devices to charge said first and second capacitors, a set of ignition points operatively connected to said first and second capacitive devices, upon closing said set of ignition points said first and second capacitive devices discharging therethrough to render said gate controlled switch non-conductive, said first capacitive device drawing current from said gate electrode and said second capacitive device drawing current from said anode electrode, with a voltage being induced in said primary winding of said ignition transformer by the gate controlled switch being rendered non-conductive, an output spark voltage being provided in said secondary output winding in response to the induced voltage in said primary winding, upon opening said set of ignition points a voltage being induced in said inductive device in said charging circuit to recharge said first and second capacitive devices to render said gate controlled switch conductive.

4. An ignition circuit comprising, a gate controlled switch including a plurality of electrodes, an ignition transformer including a primary winding operatively connected to said gate controlled switch and a secondary winding, a charging circuit, a first capacitive device operatively connected between one electrode of said gate controlled switch and said charging circuit, a second capacitive device operatively connected between another electrode of said gate controlled switch and said charging circuit, said first and second capacitive devices being charged through said charging circuit, a biasing circuit operatively connected to said gate controlled switch to bias said gate controlled switch into its conductive state, switching means operatively connected tosaid first and second capacitive devices, upon closing said switching means said first and second capacitive devices discharging therethrough to render said gate controlled switch nonconductive, a voltage being induced in said primary winding by said gate controlled switch being rendered nonconductive, an output spark voltage being induced in said secondary winding in response to said voltage, said gate controlled switch being rendered conductive through said biasing circuit after a predetermined time, upon opening said switching means said first and second capacitive de- Vices recharging through said charging circuit.

5. An ignition circuit comprising, a gate controlled switch including anode, cathode, and gate electrodes, said cathode electrode operatively connected to a reference potential, an ignition transformer including a primary windi-ng operatively connected in series to the anode electrode of said gate controlled switch and a secondary winding, a charging circuit including an inductive device, afirst capacitive device operatively connected between the gate electrode of said gate controlled switch and said inductive state, a set of ignition points operatively conductive device of said charging circuit, a second capacitive device operatively connected between the anode electrode of said gate controlled switch and said inductive device of said charging circuit, a biasing circuit operativ'ely connected to the gate electrode of said gate controlled switch to bias said gate controlled switch to be rendered conductive, a set of ignition points operatively connected to said first and second capacitive devices, upon closing saidset of ignition points said first and second capacitive devices discharging theretbrough to cause said gate controlled switch to be rendered non-conductive a first voltage being induced in said primary winding by said gate controlled switch being rendered non-conductive, an output spark voltage being induced in said secondary winding in response to said first voltage, said gate controlled switch being rendered conductive through said biasing circuit after a predetermined time, upon opening said set of ignition points a second voltage being induced in said inductive device to recharge said first and second capacitive devices.

6. An ignition circuit operative with a source of direct current comprising, a gate controlled switch including anode, cathode, and gate electrodes, said cathode electrode operatively connected at a reference potential, an ignition transformer including a primary winding operatively connected between said source of direct current and the anode nected to said first and second capacitive devices, upon closing said set of ignition points said first and second capacitive devices discharging therethrough to render said gate controlled switch non-conductive, said first capacitive device drawing current from said gate electrode and said second capacitive device drawing current from said anode electrode of said gate controlled switch, a first voltage being induced in said primary winding by said gate controlled switch being rendered non-conductive, an output spark voltage being induced in said secondary winding in response to said first voltage, said gate controlled switch being rendered conductive through said biasing circuit after a predetermined time, upon opening said set of ignition points a second voltage being induced in said inductive device to recharge said first and second capacitive devices.

References Cited by the Examiner UNITED STATES PATENTS 3,197,716 7/1965 Wright et al. ;30r/-ss.5 3,213,320 10/1965 Worrell s15' -209 J. ZAZWORSKY, L. M. GOODRIDGE,

' Assistant Examiners. 

1. AN IGNITION CIRCUIT COMPRISING, A GATE CONTROL SWITCH INCLUDING A PLURALITY OF ELECTRODES, AN IGNITION TRANSFORMER SERIES WITH SAID GATE CONTROLLED SWITCH AND A SECONDARY OUTPUT WINDING, A FIRST CAPACITIVE DEVICE OPERATIVELY CONNECTED TO ONE ELECTRODE OF SAID GATE CONTROLLED SWITCH, A SECOND CAPACITIVE DEVICE OPERATIVELY CONNECTED TO ANOTHER ELECTRODE OF SAID GATE CONTROLLED SWITCH, A CHARGING CIRCUIT OPERATIVELY CONNECTED TO SAID FIRST AND SECOND CAPACITIVE DEVICES TO CHARGE SAID FIRST AND SECOND CAPACITIVE DEVICES, A SET OF IGNITION POINTS OPERATIVELY CONNECTED TO SAID FIRST AND SECOND CAPACITIVE DEVICES, UPON CLOSING SAID SET OF IGNITION POINTS SAID FIRST AND SECOND CAPACITIVE DEVICES DISCHARGING THERETHROUGH TO RENDER SAID GATE CONTROLLED SWITCH NON-CONDUCTIVE, WITH A VOLTAGE BEING INDUCED IN SAID PRIMARY WINDING OF SAID IGNITION TRANSFORMER BY THE GATE CONTROLLED SWITCH BEING RENDERED NON-CONDUCTIVE, AN OUTPUT SPARK VOLTAGE BEING PROVIDED IN SAID SECONDARY OUTPUT WINDING IN RESPONSE TO THE INDUCED VOLTAGE IN SAID PRIMARY WINDING, UPON OPENING SAID SET OF IGNITION POINTS A VOLTAGE BEING INDUCED IN SAID CHARGING CIRCUIT TO RECHARGE SAID FIRST AND SECOND CAPACITIVE DEVICES. 